Members of the MPE family are found in a large variety of
Gram-negative and Gram-positive bacteria . They consist of 370-420 amino
acyl residues with 9 (RodA) or 10 (FtsW) putative transmembrane
α-helical spanners. Experimental evidence for a 10 TMS model has been
reported for FtsW of Streptococcus pneumoniae (Gérard et al., 2002). The S. pneumoniae protein has both its N- and C-termini in the cytoplasm, a large (~60
residue) cytoplasmic domain between TMSs 4 and 5, and a large (~80
residue) extracytoplasmic loop between TMSs 7 and 8.

The best characterized members of the family are the FtsW cell
division protein, the RodA rod shape determining protein (both of E. coli) and the SpoVE protein of B. subtilis (Boyle et al. 1997; Errington, 2003; Matsuzawa et al., 1989; Sato et al., 1990). They have been shown to function in the translocation (export) of
lipid-linked murein precursors such as NAG-NAM-pentapeptide
pyrophosphoryl undecaprenol (lipid II) (Mohammadi et al. 2014). They interact with murein
synthases as well as two transpeptidases (PBP2 and PBP3). In
Gram-negative bacteria the ftsW gene is physically linked to murG (TC# 9.B.146) which is responsible for the final cytoplasmic step in the synthesis of
lipid II before it is flipped to the periplasmic side of the membrane.
They may therefore be part of a tunneling device directing the flow of
murein precursors to the membrane enzymes that insert the precursors
into the preexisting murein sacculus.

Bacterial cell growth necessitates synthesis of peptidoglycan.
Assembly of peptidoglycan is a multistep process starting in the
cytoplasm and ending in the exterior cell surface. The intracellular
part of the pathway results in the production of the membrane-anchored
cell wall precursor, Lipid II. After synthesis, this lipid intermediate
is translocated across the cell membrane. The translocation (flipping)
step of Lipid II requires a specific protein (flippase). Mohammadi et al.
(2011) showed that the integral membrane protein FtsW, an essential
protein for cell division, is a transporter of the lipid-linked
peptidoglycan precursors across the cytoplasmic membrane. Using E. coli membrane vesicles, they found that transport of Lipid II requires the
presence of FtsW, and purified FtsW induced the transbilayer movement of
Lipid II in model membranes.